Currently, setting of the audio output level for a device equipped with an audio output, such as a television set or audio equipment, is generally made through remote control with a remote control unit, as well as through setting with the main unit of the device. Therefore, the main unit and remote control unit each have up/down buttons for the volume level, where these volume change buttons are operated as required when using a television set or audio equipment. A volume adjustment button is usually easy to operate because it is frequently used.
Meanwhile, a television set or audio equipment usually has a volume range from an adequately large volume, as compared to a volume in regular use, to silence. The maximum available volume of the device is not necessarily equal to a normal level in regular use.
Among conventional methods of setting the audio output level, a method of automatically adjusting the volume level according to ambient circumstances is disclosed in Japanese Patent Unexamined Publication No. H08-97654 (hereinafter, referred to as “patent literature 1”). Further, a method in which minimum and maximum input levels are preliminarily set when amplifying audio signals with a variable gain amplifier is disclosed in Japanese Patent Unexamined Publication No. H10-294990 (hereinafter, referred to as “patent literature 2”).
As mentioned above, the operation of changing the volume setting for a television set or audio equipment is desirably easy because the operation is frequently performed. This may cause the volume level to increase more than necessary if the operable part is accidentally touched or if an infant innocently changes the volume level.
Even if the volume level is automatically changed according to ambient circumstances as in the invention described in patent literature 1, the above-mentioned problems cannot be solved because the basic audio level is set by the user.
Meanwhile, a maximum output volume may be restricted as in the invention described in patent literature 2, which poses an obstacle because a required volume level may not be available in some operation environments.
Further, in a television set or audio equipment, turning on the power again after turning off the power with the volume level at a high setting causes too large a sound to burst out from the device because the previous audio output level is retained.
Another problem is, if the audio output level has been changed while the device is controlled to be in a silent state, ending the silent state unexpectedly causes too large a sound to burst out from the device.